Potential recording mechanism



Nov. 18, 1941. F. OFFNER POTENTIAL RECORDING MECHANISM Filed Feb. 17,1939 3 Sheets-Sheet 1 AInp/If/ er Recorder awe/mm:

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POTENTIAL RECORDING MECHANISM Filed Feb. 17, 1939 3 Sheets-Sheet 2 Nov.18, 1941. F. OFFNER 2,262,958

POTENTIAL RECORDING MECHANISM Filed Feb. 17, 1939 3 Sheets-Sheet 3 I 4A29 o o 5i i I I a 2 23, 30 Q i I g (1 f Hg Q a/ z 32 33 $29 ea {2 o 0rem-J- Patented Nov. 18, 1941 UNITED STATES PATENT; OFFICE azsaossPOTENTIAL RECORDING imcnA rsM Franklin Oifner, Chicago, 111. ApplicationFebruary 17, 1939,; Serial No. 257,005

(Cl. ass-5.5)

3Claims.

This invention relates to improvements in e1ec-- tric potentialrecorders and particularly to improvements in direct recordingelectrocardiov graphs.

An object of the present invention is to pro- .vide for more faithfulrecording at higher frequencies and with larger amplitudes than haspreviously been possible.

Another object of the invention is to provide a novel form of couplingbetween the piezo-electric crystal elements and the recording element.Other objects and advantages of the invention will be evident from thefollowing description the line thereof adjacent each other. Thepiezo-electric crystal units 2| and 22 are preferably of the typedisclosed in the patent to Alfred L. Williams No..

2,105,011 dated January 11, 1938, and are provided at each of threecorners with metal bearing plates 23 on the front face thereof whichbearing plates are formed to provide ball-like protuberances or pivotbearings 24. These pivot bearings contact the inner face of the coverplate I! of the casing-l3 and are held firmly in contact therewith byresilient rubber blocks 25 dis-.

posed between the rear wall of the casing-and each of the said threecomers of the crystals' which are provided with bearing plates 23. Athin layer of rubber 28 is disposed between each of-the bearing plates23 and the surface of the crystal elements. when the crystals aredisposed in the casing as shown in Figs. 4 and 5 and the cover plate I:is applied and the screws 21 which secure the cover plate in position,are tightened, the crystal units are firmly supported between the coverplate and the rear wall of the casing, being clamped between the bearinplates 23 and the rubber blocks 25.

with three corners of each of the rectangular crystal elements 2! and 22clamped as described Fig. 6 is a diagrammatic illustration of anelectrocardiograph recording system embody g the v invention, and

Fig. 7 is an illustration of a calibration record produced by theinvention.

The recording mechanism shown in Figs. 1 to 5 is mounted on a cabinetill, the top of which is formed of a metal plate ll which forms a basefor mounting the various elements of the recorder.

The recording pen assembly is mounted on the front cover plate I! of anupstanding casing ll.

Thecasing II is pivoted at one end thereof on a horizontal stub shaft l4carried by a block ll mounted on the plate H. A bored block ll securedto the side of the casing by screws ll slides on the shaft l 4 to effectthe pivotal mounting. A locking set screw ll secures the casing inaxially adjusted position on the shaft II. The other end of the casingll rests on an adjustable stop in the form of a set screw I! threadedinto. the plate II which provides a means for adjusting the elevation ofthe casing and thus the contact pressure of the recording point on.therecord tape. 7 a

The recording pen arm 20 is actuated by a pair' of piezo-electriccrystal bending units II and 22 mounted in substantially the same-planewithin the casing ll with the driving points above, the free corners IIand 2| respectively, which are disposed adjacent each other are free tomove in response to any piezo-electric deformation in the crystal unitsproduced by the application of electrical potential thereto. The fourthand movable corners of the crystal units are provided with metal clips3| and II, respectively, which engage over the corners and are cementedin position. Each of the clips or corner pieces Ill and II carries aphosphor bronze strip in the formof a projecting arm disposed at rightangles to the face of the crystals. These arms, designated 32 and II,respectively, have connected in parallel but in such sense that when anE. M. F. is applied, the free corners II and II thereof move in oppositesense so that the arms 82 and 33 move along substantially parallel pathsin opposite directions.

Because of the relatively small deformation of the crystal unitsthemselves and the correspondingly slight movement of the arms 32 and 33carried by the movable corners thereof, it is-necessary to provide for alarge mechanical multiplication of this motion. In orderto eflect thismultiplication of the crystal motion, the forward ends ofthe arms 32-and33 are connected to opposite sides of a rocking member in the. form of asmall pulleyelement 35 which is formed with, or rigidly connected with,a coaxial larger pulley segment 36. The ends of the arms 32 and.

33 are preferably soldered to opposite sides of the pulley 359sindicated at Hand 38. The diameter of the small pulley 35- is preferablyabout 4 inch and that of-the large pulley segment about 1% inches. Theduelpulley 35-36 is carried on a pivot shaft 39 which is. journalledin'jewel bearings 40 and 4| mounted in a supporting block 42 rigidlysecured. to the face of the cover plate l2. s

The supporting arm "for the marking element is carried on a pivot shaft43 the pointed hardened ends of which are journalled in cup jewelbearings 44 and 45 mounted-in the opposed endsof screw members 46 and 41adjustable in the projecting arms of brackets 48 and 49 tightening ofthe screw 52v tends to draw: theblock 58 up to the block 42.

The screw 53. is threaded through the block 50 and its inner endbearsagainst the surface of block 42 so that tightening the screw 53tends to force the blocks 42 and 50 apart. By relative adjustment of thescrews, the position of the block 50 can be adjusted and locked due tothe opposing forces exerted by the screws.

The pivot shaft 43 is parallel to the pivot shaft 39 carrying thepulleys 35 and 36 and is provided with a'small pulley 54 in horizontalalinement with the pulley segment 36. -A very thin'brass band 55 havingits opposite. ends fastened to the pulley segment 36, as by small hooks56 and 51 mounted at the ends thereof, is trained casing |3 to provide aseal at this joint.

It has been found thatthe use of two crystalline elements connected tomove in opposite sense as above described possesses several advantages.First it provides double the power of a single element which allows'theamplitude of motion of the marking element to be increased by the factorthe square root of two, while maintaining the same frequency response,or allows the frequency response to be increased by the same factorwhile maintaining the same available amplitude. Also, due to theconnections employed where the amplitude of motion of each crystalelement is exactly the same, a pure torque is supplied to pulley 35 andpulley segment 36 so that in theory, the shaft and bearings for thesepulley elements could be dispensed with entirely, and in actual practicesome slight play in these bearings will not result in any'lost motion inthe system. Great care in avoidance of any possibility of lost motion inany portion of the mechanical system is particularly important'in apiezo-electric crystal actuated recording system of this type becausethe motion of s the crystals themselves is so minute. as compared withthe final resultant motion of the marking point. Thus a lost motion of.001 inch between the crystals and the segment due to play in thesegment bearings would result in lost motion of 0.1 inch at the markingpoint, assum- I ing a ratio of 100 tol, a representative value. It willbe noted that with the mechanical system herein disclosed, all parts ofthe system are under tension and thus no lost motion can occur in anypart thereof.

The travelingtape 65 for receiving the record 7 'is served from a roll66 mounted within the cabinet IO, passing over tensioning guide rods 61,through a slot '68 in the base plate I and thence over the surface ofthe plate between upper and lower feed rolls 69 and 18, respectively.The uparound the pulley 54 on the pivot shaft 43 for The diameter of the.justin'g the-screws52 and 53 the block 56 may be disposed and locked inposition to adjust the tension of the pulley band 55. I a

The supporting arm 20 for the marking element. 5'8 is;preferably madefrom a duralumin stamping about .002 of an inch thick and carries a'small ink tube 59 connected to the writing point 58 mounted at the endthereof. Ink is carried to thisassembly through a fine rubber tube 60from an ink well 6| carried on a post 52 and adjustable in height tovary the ink pressure supplied to the writing point.

Since the crystal elements may be affected by moisture, it is desirablethat the container |3 be tightly sealed. To effect this, a flexiblerubber opening 34in the cover plate l2 and the motion transmitting arms32 and 33 project through per tape feeding roller 69 is mounted on ashaft 1| journalled in bearings 12 mounted on the plate while the lowerroller 18 is mounted on a shaft 13 journalled between the free ends ofspaced arms 14, the other ends of which are pivoted on a bracket 15 onthe underside of the plate Tension adjusting screws 16, threaded intothe respective arms 14 adjacent their freeends extend through openings11 in the plate II and have springs 18 confined between the heads.

of the screws and the surface of the plate. Tightwing or loosening thescrews 16 results in varying the pressure between the rollers 69 and 10.

The tape feeding roller 69 is driven, by a synchronous motor 19 througha variable speed .drive. The motor 19 is provided'with a built onreduction gear drive 80 on the output shaft 8| of which gears 82 and 83are mounted. The gear 82 is the larger of the two and is adapted to meshwith a smaller gear 84 on the shaft 1| of roller 69 while the gear '83is smaller and is thisdiaphr'agm, being sealed-thereto by rubbercement.A suitable gasket 64 is also disposed beadapted to mesh with a largergear 85 also mounted on shaft 1|, as shown in Fig. 1.

In order to provide for shifting the gears 82 and 83 selectively toengage them with the respective gears 84 and 85, themotor 19 is mountedon parallel links 86 and 81, pivoted at one end on the plate H asindicated at 88 and having pivotal connection to the'motor base asindicated at 89.

serves for swinging the linkage mechanism to shift the motor and gearassembly including the The link 81 extends beyond theedge of the plate Ito provide a handle 98 which.

, between 90 and M. A series of switches 93, 04,

.is interposed between the primary and secondary.

I I capacity coupled: type having a variable voltage gears 82 and v83 sothat either one of the latter may be engaged selectively with itsassociated gear 04 or 85.

;The electrical circuit connections for use of this potential recordingmarker in electrocardiog- 5 raphy are shown in Figure 6. Here 90represents the writing mechanism described above, a thermionic vacuumtube amplifier, and 92 a variable series resistance element placed inseries 85 and Stare used to connect the proper pairs of patientelectrodes from the four standard electrical lead positions, right arm,left arm, chest and left-leg, to the amplifier input terminals.

These patient electrodes are numbered 91, 98, 99 and ill, respectively.'

A calibrating means MI is interposed in series .with the amplifierinput. This is so arranged that direct potential pulses of l millivoltamplitude or an alternating potential of'l millivolt peak amplitude maybe alternatively introduced.

One way of constructing such a calibrating means is indicated in Fig. 6.A resistor I0! is interposedin series with the input of the amplifierand either a direct current or an alternating current; may alternativelybe passed through this resistor by throwing switch I03. The D. C. isobtained from'battery- I04 and the current as read on meter H4 isadjusted by variable resistor I05 so thatits value is sumcient to givethe proper voltage drop in resistor I02. The A. C. is obtained fromtransformer I06, the primary of which'is connected to a 60 cycle A. C.supply line. A grounded electrostatic shield Ill 30 Here againthecurrent'jwhich is" passed through resistor lill-"isadjusted to theproper value as read on meter I ll, by a 'variable resistor I08. Nowwhen switch-J03 is rapidly opened and closed in the down; position aseries of D. C. pulses is 40 applied to thezamplifier input, whilethrowing the switch in the'up;position will apply an alternatingcurrent. "The function of this will be discussedlater.

Theamplifierfis'preferably of the resistance 4:;

gain of. up tofabout three hundred thousand times and an overall timeconstant of approximately one totwoseconds. It should be capable of.delivering a peak output voltage of about six hundred volts and itsoutput impedance should be under approximately forty thousand ohms. Thepurpose of the variable series resistance element 9! is to providedamping of the motion of the recorder. The leads I" and H0 from theamplifier may be connected to the crystals through binding posts HI andH2.

Damping is required in this recorder because the moving mechanicalsystem attached to the crystals has such relatively large inertialeffectit will reduce the resonant frequency of the system composed of thecrystals andmechanical system to a frequency approaching that which itis desired to record. Although this moving sys-' tem be made as light aspracticable, such an in- 05 ertial effect will still be produced, fortheamplitude of motion of. portions of the system, and especially of member20 and associated marking element and ink tube, is relatively very greatas compared with the motion of the crystals. The 70 effective inertia ofany portion of the system is found by multiplying; its actual mass bythe square of its amplitude of motion; and thus it is seen that the massof the marking element may be 100 or 10,000 times as important as anequal mass at the driving point' of the crystal itself. The totalinertial efiect of the moving mechanical system in the instrument ashere described, is such that the mass of the crystals themselves isnegligible in comparison therewith.

Now assuming that there were no damping introduced in theelectro-mechanical system, as the resonant frequency is approached theamplitude of motion produced by a constant input voltage would greatlyincrease, and thus give distorted records of waveform. However, byproperly introducing damping means, either electrical or mechanical, itis possible to dissipate relatively more power in such means as theresonant frequency is approached, and by careful adjustment of thismeans a relatively uniform response amplitude may be obtained,independent of frequency, even up to frequencies slightly surpassing the-first electro-mechanical resonant frequency of thesystem. As previouslydisclosed, it is possible to obtain such damping by the use of such aseries resistance, and applicant has found that in the present inventionis is desirableto obtain damping. of the motion by this 7 means inpreference to mechanical damping. Applicant has found that the optimumvalue of this resistance may be very simply found by the use ofcalibrator Ill. A direct potential of 1 millivolt is introduced and theresponse amplitude adjusted to a suitable value (c. g. 1 cmas standardfor electrocardiography) by varying the amplifier gain. Now analternating potential of this same peak amplitude is introduced and thedamping resistor 92 is adjusted until the re sponse amplitude obtainedfrom the alternating potentials is equal to that obtained with thedirect potential. The appearance of records when properly damped isshown in Fig. 7. Here H6 represents the form of tracing which would beobtainedwith the direct current pulses and Ill that-obtained with thealternating current. The

- frequency of alternating current to be here used is not critical butshould lay in the middle range of the instrument. 60 cycles per secondis a suitable value. Thejustification for this method of damping is asfollows: The most desirable form of frequency response for a recorder isone in which all frequencies are recorded with equal amplitude (assumingthey are of the same voltage). Applicant has found that if directcurrent pulses (in effect very low frequencies) and medium frequencypotentials (as here 60 cycles per second) are recorded with the sameamplitude-the frequency response curve of the instrument is made asnearly flat as possible. A variation of the damping resistor 92 will notaffect appreciably the amplitude of the direct current pulses because ofthe relatively high impedance of the recorder to direct current, andthus the calibration need not be reset after adjusting the dampingcontrol. Although the voltages supplied for adjusting the dampingare'here shown in series with the input they may be alternativelyinserted in any positions in the system so long as they introduce equalvoltages in series with the the body in the four positions indicated,and a pair of the switches 63- are closed to connecta selected pair ofelectrodes to the input terminals of the amplifier. The recording pointwill mark a direct record of the wave form of the body potentials asmodified by the heart action so as to produce a cardiogram suitable fordiagnosing the condition of the heart. Calibration may also be performedwith the patient in the circuit, with switch 3 open.

Although a preferred embodiment of the invention and manner of employingthe same have been illustrated and described by way of example, it willbe understood that various modifications of the details of constructionand mode of opera- .tion may be resorted to without departing from thespirit of the invention within the scope of the appended claims.

I claim:

1. In a potential recording mechanism of the character described, a pairof piezo-electric crystalline elements supported with the driving pointsthereof adjacent each other and connected to a current source in suchmanner that said driving points move in opposite directions under the Vaxis of said rocking member, said connections each comprising arelatively stiff link rigidly fastened at one end to one of said drivingpoints and rigidly fastened at its other end to said rocking member, a'pivot shaft spaced from the axis of said rocking member andsubstantially parallel thereto, a small diameter pulley member on saidpivot shaft, a flexible band providing a driving connection between saidrocking member and said pulley member, a recording arm carried by saidpivot shaft and a marking element adjacent the free end of said am.

3. In a device for making direct legible marked records of the wave formof varying electricalpotentials, a plurality of piezo-electric'crystalelements connected in reverse parallel relation with the source of saidpotentials, and having movable portions adjacent each other, apivotedrecording arm, motion multiplying means pro: viding a driving connectionbetween said crystal elements and said recording arm, said drivingconnection comprising a rocking unit including a pair of coaxial rockingpulley members of differpivoted recording arm, and tensioned drivingconnections between said said recording arm.

2. In a device for making legible marked records of the wave form ofvarying electrical potentials, a pair of piezo-electric crystal unitssupported with the free ends thereof adjacent and connected with thecurrent source in reverse relation so as to respond in opposite senseunder the influence of applied electrical potential, a

rocking member and ent diameters, a relatively stiff projecting armrigidly secured at one end thereof to the movable portion of eachof saidcrystal elements, said arms being rigidly connected at the other endthereof to the pulley member of smaller diameter on opposite sides ofthe axis thereof to provide a positive two-way drive connectionbetween'the movable portion of each .crystal element and the rockingunit whereby said crystal elements mutually aid each other in impartinga rocking pivoted rocking member, two-way motion trans- I mittingconnections'from the free ends of said crystal units to points onopposite "sides of the action without lost motion to said pulleymembers, a pivot shaft for said recording arm disposed substantiallyparallel with the axis of said pulley members, a pulley member carriedby said pivot shaft having a diameter less than that of the larger ofsaid first mentioned pulley members,

and a flexible driving connection between the peripheries of the largerof said first mentioned pulley members and the pulley on said pivotshaft.

FRANKLIN OFFNER.

